An EFI (Electric Fuel Injection) system having a feedback control function and using an O.sub.2 sensor as an exhaust sensor inputs an O.sub.2 concentration detection signal from the O.sub.2 sensor into a control means which feedback controls the air-fuel ratio to a predetermined value in accordance with the O.sub.2 concentration.
One conventional example has a single point fuel injection valve, and effects feedback control by an O.sub.2 sensor at a steady run when in a normal acceleration as shown in FIG. 3. When the air-fuel ratio (A/F) becomes 14.7 and it is brought into an acceleration state during running, acceleration increase is preformed for a certain time. Since it enters into a power area, the air-fuel ratio becomes 13 or less (see FIG. 3(c)).
At this time, the O.sub.2 sensor continuously outputs rich signals at a certain delay from the moment it is shifted to acceleration (see FIG. 3(a)).
However, if an attempt for acceleration is made using fuel low in distillation, i.e. heavy gravity fuel, in the same manner as mentioned above, delay occurs when air-fuel mixture is fed into the combustion chamber owing to inferior volatility of the heavy gravity fuel after the accelerator is opened. This becomes a factor for causing waver, stumble, etc. owing to leaning of the air-fuel ratio. Finally, it sometimes results in stalling of the engine.
This phenomenon significantly appears especially when in cold operation and occurs more easily as the distance from the fuel injection valve to the combustion chamber becomes longer when the fuel injection valve is disposed further upstream from the throttle valve.
As shown in FIGS. 3(b) and 4(b), the aforementioned problems can arise, for example, during an attempt to accelerate from a given steady running condition to another, higher speed steady running condition.
Fuel used in the United States of America is, in general, very wide in range such as 80.degree..about.120.degree. C. at the 50% distillation point. For example, if a usual normal setting is effected when fuel of either of the two extremes is used, drivability is extremely deteriorated.
That is, in the conventional general system, correction is not made at all when heavy gravity, low volatility fuel is used, and the values of post-start increase, acceleration increase, etc., when in cold operation must be set large anticipating the use of heavy gravity fuel.
A distinction device of fuel being used by an internal combustion engine is disclosed in Japanese Patent Early Laid-Open Publication No. sho 63-162951. According to a method disclosed in this publication for controlling the ignition timing and air-fuel ratio of an internal combustion engine, the ignition timing is spark controlled when the octane number of fuel in use is high and the air-fuel ratio is feedback controlled to a target air-fuel ratio in accordance with the output of the O.sub.2 sensor. The air-fuel ratio is controlled to be more rich than the target air-fuel ratio when the octane number of fuel in use is high, and NO.sub.x is reduced to obtain a favorable exhaust emission without lowering engine output when fuel of a high octane number is used.
The conventional device does not have a correction function for distinguishing the properties of fuel and effecting control which is fitted to the properties of heavy gravity fuel. It does not have a function for learning such distinguished properties of fuel, either. Therefore, if the values of post-start increase, acceleration increase, etc. are preset to be large, anticipating the use of heavy gravity fuel, the air-fuel ratio becomes over-rich when usual fuel of average volatility is used, drivability becomes worse, a large amount of hazardous exhaust gas is discharged as the drivability becomes worse, and the function of cleaning exhaust gas is also impaired.
On the contrary, if the values of post-start increase, acceleration increase, etc. are set without anticipating the use of heavy gravity fuel, engine stall and significant deterioration of drivability arise after the start of the engine when heavy gravity fuel is used. This is disadvantageous in view of practical use.
In order to reduce the above-mentioned inconveniences, it is an object of the present invention to provide a distinction device which distinguishes fuel in use by an internal combustion engine, comprising control means for distinguishing fuel in use as heavy gravity fuel when lean signals of air-fuel ratio are sequentially output for a predetermined time or more at the start of increased fuel supply during acceleration of an internal combustion engine, and for learning properties of the fuel in order to control the air-fuel ratio depending on the fuel, thereby enabling the air-fuel ratio to be set as necessary for heavy gravity fuel when said control means has distinguished that the fuel in use is heavy gravity fuel. As a result, the occurrence of waver and engine stall during acceleration can be prevented, the acceleration increase is not required to be preset in all cases to a large value anticipating the use of heavy gravity fuel, and drivability can be maintained in an excellent state irrespective of the fuel in use.
The present invention is used in an internal combustion engine for effecting feedback control in order to enrich the air-fuel ratio during acceleration by increasing the supply of fuel when accelerating, and comprises control means for distinguishing fuel in use as heavy gravity fuel when lean signals are sequentially output for a predetermined time or more when the fuel supply is increased during acceleration, and for learning the properties of said fuel in order to control the air-fuel ratio depending on such learned properties.
By virtue of the above-mentioned construction, when lean signals of air-fuel ratio are sequentially output for a predetermined time or more at the start of increased fuel supply during acceleration of the internal combustion engine, the fuel in use is distinguished as heavy gravity fuel by control means, properties of the fuel are learned in order to control the air-fuel ratio depending on the learned properties, the air-fuel ratio is set corresponding to the heavy gravity fuel, occurrence of waver and engine stall during acceleration can be prevented, the amount of acceleration increase is not required to be preset in all cases to a large value anticipating the use of heavy gravity fuel, and drivability is maintained in an excellent state irrespective of the fuel in use.